Dynamic antenna tuning apparatus and method

A near-field transmitter for transmitting a signal using near-field communication, comprising:

• a modulator having an input for receiving a communication signal, and an output for providing a differential output signal to first and second integrated circuit terminals;
• a power amplifier having an input coupled to said output of said modulator, and first and second outputs adapted to be coupled to an inductor, for providing a differential output signal;
• a tunable reactive element coupled between said first and second outputs of said power amplifier whose reactance is tuned by a tuning signal;
• an envelope detector coupled to said output of said power amplifier for providing an envelope signal in response to said differential output signal;
• and
• an antenna tuning circuit for adjusting said tuning signal in response to said envelope signal.

A method of tuning a radio transmitter, comprising:

• forming a communication signal at a carrier frequency;
• amplifying a power of said communication signal and forming a differential output signal in response to said amplifying;
• providing said differential output signal to a resonant network having a tunable reactive element;
• rectifying said differential output signal to provide a rectified signal;
• determining a level of said rectified signal;
• and
• adjusting a value of a reactance of said tunable reactive element to an optimum amplitude of said rectified signal during operation of the radio transmitter.